Resin types: Water Soluble vs PLA

Question

With resin LCD printers (not filament!), what are the considerations to choose between PLA and "water soluble"? Microcenter carries resins from esun in these two types, and their spec sheets indicate that tyhe water-soluble type has higher tensile strength and other mechanical properties. Which leads me to wonder, under what circumstances one selects PLA then?

Answer 1

First of all, let's look at what the filaments are:

PLA & PVA Filaments

Normal PLA and Water-soluble PVA contain for the most part the material on the tin, its precursors, and possibly some modifiers. These are only suitable for thermoplastic processes like injection molding or FDM/FFF (Filament deposition modeling/Fused Filament Fabrication) printers - the finished polymer can't be made back into a UV-curable resin easily. Both materials are chemically rather well bonded and are not very reactive at all. They are biodegradable and not a lot of toxic waste. PLA needs very strong chemicals such as dichlormethane to go into solution, but PVA is water-soluble.

Resin

Almost no cured resin (as in post-polymerized) is water-soluble, your webshop might have a misnomer as it meant to write the proper name: water-washable, which is meant to reflect the ability to put the unpolymerized monomers into solution in water.

eResin

eSun offers an eResin-PLA-Bio-Photopolymer, which is similar to PLA, but it is not the same material you get for an FDM printer. You see this most easily by checking the density and the MSDS: Real PLA has a density of 1.21–1.43 g/cm³, eResin (as the bottles are labeled) has a density of merely 1.07-1.13 g/cm³. This is a totally different material in the bottle! It is most likely a resin mix that is based on lactic acid monomers and a UV-active acid that can bond the monomers, creating a structure that does contain lactic acid groups and the binder - but most certainly it is not chemically identical to PLA. It contains, according to the MSDS, Polyurethane acrylate as the 'binder', 1,6-Hexanediol diacrylate Monomers, and about 10 % photo inhibitors and pigments. The main selling point seems to be, that comparable to PLA, it would be made from a renewable source to a larger part. The chemical reaction that leads to the completed resin is a question I have pitched on Chemistry.SE.

It needs to be cleaned with IPA (isopropyl alcohol) or another organic solvent like any standard resin and you are not allowed to rinse the material into the sewer: it is classed as a LONG-TERM AQUATIC HAZARD - Category 4 and its MSDS contains:

Solubility：Soluble in ethanol, ethyl acetate, benzene and other organic solvents, insoluble in water

water-washable eSun Resin

eSun offers no water-soluble resin at all, they offer a water washable resin, which means that it is supposed to be less toxic than standard resin and safe to rinse effectively without IPA, creating less toxic waste in the process. The MSDS for this is not (yet)) available so I can't evaluate this. However, I have requested the MSDS for the evaluation of safety procedures needed and hope to hear back from them soon. This resin is most certainly not PVA, but it seems to be chemically somewhat similar to their other resins.